A/T - 700R4 TCC Lock-Up Delay Valve

TSB 89-21 (July)

SUBJECT: THM 4L60/THM 700-R4

SUBJECT:
"Lock-up Delay Valve" (Converter Clutch Throttle Valve)

Very often it is necessary to delay lock-up in 700-R4's. To delay lock-up, many people are installing the GM converter clutch throttle valve. (# 8642970)

This valve was designed by General Motors to delay lock-up on 82-83 6.2L DIESELS that had a rattling noise from locking-up too early.

Using this valve with gas engines is causing the following problems:

PROBLEM # 1:

Torque converter severely overheats causing complete transmission failure.

PROBLEM # 2:

Engine lugs going up hill. If you give it enough gas to release lock-up, then it also kicks down to 2nd.

CAUSE OF PROBLEM # 1:

700-R4 gas engine governors do not produce enough governor pressure to operate the diesel converter clutch throttle valve properly. (See TSB 86-14)

CAUSE OF PROBLEM # 2:

The 8642970 valve was redesigned to have less area for throttle pressure to act upon. This means it takes two to three times more throttle pressure to get kickdown out of lock-up. Two to three times more throttle pressure is usually enough to cause a 3-2 kickdown, also.

POINTS TO REMEMBER ABOUT LOCK-UP SPEED:

1. If we have lock-up in 2nd gear, the transmission will run hot because the planets are in reduction, and cooler flow is reduced (orificed) in lock-up.

2. If we delay lock-up too much we could be operating in fourth gear without lock-up, which will severely over-heat the converter and burn up the transmission. (which is why we can't use the 8642970)

3. Lock-up should happen while in third gear -- probably half-way between the 2-3 and 3-4 shifts.

SOLUTION:

If you need to delay lock-up in an 82-85-21 gas vehicle, put in a heavier converter clutch throttle valve spring. DO NOT use the 8642970 valve in gas vehicles.

Here's how to select the right spring; Weigh the original spring @ .615" working height.




Use the formula to get the correct replacement spring.